Thermal unimolecular isomerization of tricyclo[4,1,0,01,3]heptane

Abstract

The thermal isomerization of tricyclo[4,1,0,0^1,3]heptane to a mixture of 3-methylenehexa-1,5-diene and hepta-1,2,6-triene has been investigated in the gas phase in the temperature range 423–463 K. In an ‘aged’ Pyrex reaction vessel, the isomerizations are homogeneous and first order, and the rate constants are independent of pressure down to 25 N m^–2. The rate constants for isomerization to 3-methylenehexa-1,5-diene fit the Arrhenius equation k₃= 10^{14·21 ± 0·12} exp(–148,800 ± 1050 J mol^–1/RT) s^–1 and those for the isomerization to hepta-1,2,6-triene fit the equation k₁= 10^{14·07 ± 0·33} exp(–155,800 ± 2760 J mol^–1/RT) s^–1 The results suggest both transformations are unimolecular and the possible transition states are discussed.